1、 ISO 2013 Water quality Determination of selenium Part 2: Method using hydride generation atomic absorption spectrometry (HG- AAS) Qualit de leau Dosage du slnium Partie 2: Mthode par spectromtrie dabsorption atomique gnration dhydrures (HG-AAS) TECHNICAL SPECIFICATION ISO/TS 17379-2 First edition 2
2、013-07-15 Reference number ISO/TS 17379-2:2013(E) ISO/TS 17379-2:2013(E)ii ISO 2013 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2013 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic o
3、r mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22
4、 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ISO/TS 17379-2:2013(E) ISO 2013 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references 1 3 Principle 2 4 Interferences 2 5 Reagents and standards 3 6 Apparat
5、us . 5 7 Sampling and sample preparation 6 7.1 Sampling technique 6 7.2 Pre-reduction . 6 8 Instrumental set-up 7 9 Procedure. 7 9.1 General requirements . 7 9.2 Analysis using the method of standard calibration . 7 9.3 Analysis using the standard addition method of calibration 8 10 Calibration and
6、data analysis 8 10.1 General requirements . 8 10.2 Calculation using the calibration curve . 9 10.3 Calculation using the standard addition method 9 11 Expression of results 9 12 Test report 10 Annex A (informative) Additional information 11 Annex B (informative) Schematic flow diagram and signal re
7、sponse 12 Annex C (informative) Example of enrichment technique 15 Annex D (informative) Performance data 17 Bibliography .18 ISO/TS 17379-2:2013(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work
8、of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-government
9、al, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the
10、ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2, www.iso.org/directives. Attention is drawn to the possibility
11、 that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of paten
12、t declarations received, www.iso.org/patents. Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. The committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC 2, Physical, chemical and biochemical
13、 methods. This first edition of ISO/TS 17379-2 cancels and replaces ISO 9965:1993, which has been technically rev ised. ISO/TS 17379 consists of the following parts, under the general title Water quality Determination of selenium: Part 1: Method using hydride generation atomic fluorescence spectrome
14、try (HG-AFS) Part 2: Method using hydride generation atomic absorption spectrometry (HG-AAS)iv ISO 2013 All rights reserved ISO/TS 17379-2:2013(E) Introduction This part of ISO/TS 17379 is intended for use by analysts experienced with the handling of trace elements at very low concentrations. Inorga
15、nic selenium normally occurs in two oxidation states; Se(VI) and Se(IV). It is essential to convert all selenium species to the Se(IV) state prior to generating the hydrides. Selenium(VI) does not form a hydride. In natural water sources, selenium compounds generally occur in very small quantities,
16、typically less than 1 g/l. Higher concentrations may be found, e.g. in industrial waste water. Selenium occurs naturally in organic and inorganic compounds and may have oxidation states II, 0, IV, and VI. In order to fully decompose all of the selenium compounds, a digestion procedure is necessary.
17、Digestion can only be omitted if it is certain that the selenium in the sample can form a covalent hydride without the necessity of a pre-oxidation digestion step. The user should be aware that particular problems could require the specification of additional marginal conditions. ISO 2013 All rights
18、 reserved v Water quality Determination of selenium Part 2: Method using hydride generation atomic absorption spectrometry (HG-AAS) WARNING Persons using this document should be familiar with normal laboratory practice. This document does not purport to address all of the safety problems, if any, as
19、sociated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions. IMPORTANT It is absolutely essential that tests conducted in accordance with this document be carried out by suitably tra
20、ined and experienced staff. 1 Scope This part of ISO/TS 17379 specifies a method for the determination of selenium. The method is applicable to drinking water, surface water, ground water, and rain water. The dynamic range of this part of ISO/TS 17379 is approximately 0,5 g/l to 20 g/l. Samples cont
21、aining selenium at higher concentrations than the application range can be analysed following appropriate dilution. The method is unlikely to detect organoselenium compounds. The sensitivity of this method is dependent on the selected operating conditions. It is important to use high purity reagents
22、 in all cases with minimum levels of selenium. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition
23、of the referenced document (including any amendments) applies. ISO 3696, Water for analytical laboratory use Specification and test methods ISO 5667-1, Water quality Sampling Part 1: Guidance on the design of sampling programmes and sampling techniques ISO 5667-3, Water quality Sampling Part 3: Pres
24、ervation and handling of water samples ISO 5667-5, Water quality Sampling Part 5: Guidance on sampling of drinking water from treatment works and piped distribution systems ISO 5667-6, Water quality Sampling Part 6: Guidance on sampling of rivers and streams ISO 5667-8, Water quality Sampling Part 8
25、: Guidance on the sampling of wet deposition ISO 5667-11, Water quality Sampling Part 11: Guidance on sampling of groundwaters ISO 8466-1, Water quality Calibration and evaluation of analytical methods and estimation of performance characteristics Part 1: Statistical evaluation of the linear calibra
26、tion function ISO 8466-2, Water quality Calibration and evaluation of analytical methods and estimation of performance characteristics Part 2: Calibration strategy for non-linear second order calibration functions TECHNICAL SPECIFICATION ISO/TS 17379-2:2013(E) ISO 2013 All rights reserved 1 ISO/TS 1
27、7379-2:2013(E) ISO 15587-1, Water quality Digestion for the determination of selected elements in water Part 1: Aqua regia digestion 3 Principle An aliquot of sample is treated with concentrated hydrochloric acid (5.2). Se(VI) is pre-reduced to Se(IV) by gently refluxing in 6 mol/l HCl for 1 h. Care
28、 is necessary to avoid any losses of volatile selenium components. A suitable apparatus is shown in Figure B.3. The sample solutions are then treated with sodium tetrahydroborate to generate the covalent gaseous hydride (SeH 2 ). The hydride and excess hydrogen are swept out of the generation vessel
29、 in the batch mode and out of the gas/liquid separator in the continuous mode into a heated silica cell. After atomization the absorbance of selenium is determined at a wavelength, = 196,0 nm. The procedure is automated by means of an auto sampler and control software. Other measurement techniques m
30、ay be applicable provided that the performance criteria can be adequately demonstrated or exceeded by the user laboratory (see Annex C). 4 Interferences The hydride generation technique is prone to interferences by transition and easily reducible metals. For the majority of natural water samples, th
31、is type of interference should not be significant. The user should carry out recovery tests on typical waters and also determine the maximum concentrations of potentially interfering elements, using appropriate methods. If such interferences are indicated, the level of interferences should be assess
32、ed by performing spike recoveries. The reaction conditions set out in this part of ISO/TS 17379 have been chosen so that any interferences are reduced to a minimum. See References 12 for further information concerning these interferences and the technique. These elements do not cause interferences p
33、rovided the concentrations specified in Table 1 are not exceeded. Table 1 Maximum mass concentrations of hydride-forming or volatile elements causing no interferences Element As Sb Sn Te Hg Mass concentration of interfering elements in test solution mg/l 1 1 0,1 1 0,1 If the concentrations in Table
34、1 are exceeded, it may be necessary to use the standard addition method (9.3). Assuming that the selenium content is high enough, an appropriate dilution of the water sample is preferred. Metals which are readily reduced by sodium tetrahydroborate may also cause interferences. In particular, these i
35、nclude chromium, iron, copper, nickel, and lead. If the concentrations of these elements specified in Table 2 are exceeded, a significant decrease of absorption may occur.2 ISO 2013 All rights reserved ISO/TS 17379-2:2013(E) Table 2 Maximum mass concentrations in test solution of interfering heavy m
36、etals (valid for flow systems) Interfering element Cr Fe Cu Ni Pb Mass concentration in test solution mg/l 500 500 500 250 100 NOTE If batch systems are used, mass concentrations which are appreciably lower than those specified in Table 1 and Table 2 can cause interferences. 5 Reagents and standards
37、 During the analysis, unless otherwise stated, use only reagents of recognized analytical grade. Reagents may contain selenium as an impurity. All reagents shall have selenium concentrations below that which would result in a selenium blank value for the method being above the lowest level of intere
38、st. Reagents shall be prepared to manufacturers recommendations using the following series as an example. 5.1 Water, complying with grade 1 as defined in ISO 3696, for all sample preparation and dilutions. 5.2 Hydrochloric acid, (HCl) = 1,16 g/ml. 5.3 Hydrochloric acid, c(HCl) = 1 mol/l. 5.4 Sodium
39、hydroxide, NaOH. 5.5 Sodium tetrahydroborate solution, (NaBH 4 ) = 13 g/l. Dissolve an appropriate amount of sodium tetrahydroborate (13 g has proven suitable for the system illustrated in Annex B) in 500 ml water (5.1) and add (4,0 0,1) g of sodium hydroxide (5.4). Dilute to 1 000 ml with water (5.
40、1). Prepare on day of use and do not keep in a closed container because of pressure build-up due to hydrogen evolution. NOTE 1 The concentration of NaBH 4is dependent on the hydride generator manifold and flow rate conditions. See recommendations of the manufacturer. NOTE 2 Suitably stored sodium te
41、trahydroborate pellets have a shelf-life of 6 months. 5.6 Nitric acid, (HNO 3 ) = 1,40 g/ml. NOTE Nitric acid is available both as (HNO 3 ) = 1,40 g/ml w(HNO 3 ) = 650 g/kg and (HNO 3 ) = 1,42 g/ml w(HNO 3 ) = 690 g/kg. Prepare a nitric acid cleaning mixture by diluting nitric acid (HNO 3 ) = 1,40 g
42、/ml with an equal volume of water (5.1) by carefully adding the acid to the water. 5.7 Reagent blank. For each 1 000 ml, prepare a solution containing (300 3) ml of hydrochloric acid (5.2). Dilute to volume with water (5.1). On the continuous flow system, the reagent blank solution is run as backgro
43、und. Since the blank solution may contain detectable trace levels of selenium, it is important that the same reagents be used for both sample and standard preparation, as well as for preparation of the reagent blank. The analyte signal is superimposed on this signal once the sample is introduced int
44、o the measurement cycle. The selenium concentration of the blank solution should be less than the lower level of interest. ISO 2013 All rights reserved 3 ISO/TS 17379-2:2013(E) 5.8 Selenium standard solutions. 5.8.1 Selenium stock solution A, Se(IV) = 1 000 mg/l. Use a quantitative stock solution wi
45、th a selenium content of (1 000 2) mg/l. This solution is considered to be stable for at least one year. NOTE Other stock solutions may be available and can be used providing the uncertainty of the measurement is not compromised. Alternatively, use a stock solution prepared from high purity grade ch
46、emicals: Place 1,094 g of sodium selenite (Na 2 SeO 3 ) dried for 2 h at (105 3) C into a 500 ml volumetric flask. Add 200 ml of water (5.1) and 200 ml of hydrochloric acid (5.3) and dissolve the sodium selenite completely by stirring. Dilute to 500 ml with water (5.1) and mix thoroughly. 5.8.2 Sele
47、nium standard solution B, Se(IV) = 10 mg/l. Pipette (1 0,01) ml of selenium stock solution A (5.8.1) into a 100 ml volumetric flask, add (30 0,5) ml of hydrochloric acid (5.2) and fill up to the mark with water (5.1). This solution is stable for one month. 5.8.3 Selenium standard solution C, Se(IV)
48、= 100 g/l. Pipette (1 0,01) ml of selenium standard solution B (5.8.2) into a 100 ml volumetric flask, add (30 0,5) ml of hydrochloric acid (5.2) and fill up to the mark with water (5.1). This solution is stable for one week. 5.8.4 Selenium standard solution D, Se(IV) = 10 g/l. Pipette (10 0,1) ml o
49、f selenium standard solution C (5.8.3) into a 100 ml borosilicate volumetric flask. Fill up to the mark with reagent blank solution (5.7). This solution shall be prepared freshly on the day of use. 5.8.5 Selenium stock solution E, Se(VI) = 1 000 mg/l. Dissolve (2,392 0,002) g of sodium selenate (Na 2 SeO 4 ) after drying at (105 3) C for 2 h in 500 ml water (5.1), then transfer the solution quantitatively to a 1 000 ml volum
